Genetics of resistance to bacterial and parasitic infection / edited by D. Wakelin and J.M. Blackwell.

Date:
1988
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Genetics of resistance to bacterial and parasitic infection / edited by D. Wakelin and J.M. Blackwell. Source: Wellcome Collection.

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    Mode of inheritance of host response 57 Table 2.16. Calculations for goodness of fit of backcross data to a single gene model using maximum likelihood (Curtis et al. 1985). The columns are calculated as follows : A Observed values for the backcross animals. (Note—^They do not need to be ranked for these calculations.) В [.?í—mean(Fl)]^/2v(Fl). From table 2.15 the mean (Fl)=2-431 and the variance is 0173 X 0-173=0-0299, and the X values are in col. A. С Calculated as e to the power, of minus the value in col. В. The value of e* is given in many arithmetic tables, and is a function commonly available in most computer languages, and advanced pocket calculators. D Calculated as the value in col. С divided by square root of 2 тг times the variance of the Fl, which is: Sqrt.(2x3 141x0 173x0-173) = 0-4336 E - G is identical to B-D, except that the mean and standard deviation for NMRI is used instead of the Fl values. H is the average of cols D and G. ^ I is the natural log of col. H. The sum of this column (-18-755) is the log likelihood of a single gene mode of inheritance. Similar calculations are necessary for the log likelihood of a polygenic mode of inheritance using the average of the Fl and P means (2-9545) and the variance of the backcross (0-3612). Using the data from table 2.15, log L polygenes = —43-073. Finally, 2(log L one gene - log L polygenes) is distributed as Chi-squared with 1 degree of freedom. In this case, the Chi-squared = 48-63, p<0 001, and we conclude that the hypothesis of a single-gene mode of inheritance is preferable to that of polygenic inheritance. being done correctly. Finally, it must again be emphasized that the finding that a given distribution of segregating progeny among classical crosses is consistent with the hypothesis of a single locus is not sufficient proof of a single-locus mode of inheritance. It is always advisable to breed from second, third, etc. backcrosses, and ideally a congenie strains should be produced, and the gene should be mapped.
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